This invention relates to a device for winding a magnetic tape in good order in a tape cassette which has been repeatedly used in e.g., a broadcasting station.
A tape cassette in general has rotatably housed therein a pair of tape reels each being made of a hub and upper and lower flange portions integrally mounted on upper and lower lateral sides of the hub. Between these tape reels is placed a magnetic tape which is paid out from a supply side reel for recording or reproduction of information signals in a recording/reproducing unit so as to be taken up on a take-up reel. The digital video tape cassette, employed for working use in e.g., broadcasting stations, employs a magnetic tape which, for assuring recording/reproduction for prolonged time, is longer in length than the tape in a typical tape cassette for personal use.
The video tape cassette, employed for reproduction in program broadcasting, is laid in store after a decision is given as to whether or not the tape cassette can be re-used based upon the channel condition represented on the basis of the error data of the playback data. Since the values of the channel conditions include all conditions from the recording conditions up to detection of digital data, they are largely dependent upon the performance of the video tape recorder and hence are not necessarily adequate for evaluation of the video tape itself. Thus, a method for evaluation has been proposed which consists of associating the status of digital errors ascribable to the video tape with the channel conditions.
The digital errors mainly ascribable to the video tape include burst errors caused by scratches in the magnetic layer of the video tape and dropout. The digital error is also caused by dust and dirt, contaminations or creases on the surface of the magnetic layer, or edge damage. Thus it is desirable that quality evaluation of the video tape be performed comprehensively for these respective items.
For reproducing the video tape cassette, the video tape is reeled out from the supply reel so as to be taken up and wound on the take-up reel. Thus the video cassette tape is rewound for enabling re-use after quality evaluation of the video tape. On the other hand, the video tape, which has been reproduced, is loaded on a tape take-up device for rewinding. During this rewind operation, the dust and dirt or contamination on the surface of the magnetic layer or powder debris are removed by way of cleaning. The magnetic tape cleaning device is usually positioned directly ahead of a point of introducing the video tape drawn out from the take-up reel to the supply reel.
On the other hand, the tape take-up device is provided with a device for taking up a video tape in a good condition on the supply side reel. The device for taking up the video tape in a good condition affords a pressure contact force against the video tape for preventing edge damage due to misalignment or air entrainment between superposed turns of the video tape responsible for crease formation. Similarly to the magnetic tape cleaning device, the device for taking up the video tape in a good condition is positioned directly ahead of the point of introducing the video tape drawn out from the take-up reel to the supply reel.
The conventional device for taking up the video tape in a good condition includes a roll arm member one end of which rotatably carries a touch roll configured for affording a pressure contact force against the magnetic tape. This roll arm member is moved with respect to the magnetic tape taken up on the tape reel for being pressure contacted with the magnetic tape.
With the conventional device for taking up a video tape in a good condition, the magnetic tape taken up on the tape reel is subjected to a contact pressure force extending in the circumferential direction of the magnetic tape taken up on the tape reel as the contact pressure force produced by the touch roll is deviated from the center of rotation of the tape reel. The result is that the magnetic tape taken up on the take-up drum is affected by excess tightness or excess slack in winding. Thus it is required of the touch roll to direct the line of force of the contact pressure against the magnetic tape towards the center of rotation of the tape reel.
If the contact pressure force exerted by the touch roll is diminished for preventing destruction of the magnetic tape by the contact pressure force, an air layer between the superposed turns of the magnetic tape cannot be removed sufficiently such that satisfactory winding state cannot be achieved.
With such device for taking up the video tape in a good condition, the touch roll is pressed against the magnetic tape by an elastic member. As the winding diameter of the magnetic tape taken up on the tape reel is increased, the amount of deviation of the elastic member is increased, with the result that the contact pressure force of the touch roll is progressively increased.
That is, as the winding diameter of the magnetic tape taken up on the tape reel is increased, the contact pressure force exerted by the touch roll on the magnetic tape taken up on the tape reel is increased. Thus, it is up to the roll arm member to shift the touch roll along the diameter of the tape reel responsive to changes in the winding diameter of the magnetic tape.
In addition, the magnetic tape for work use for recording/reproduction for a prolonged time has a long tape length and an extremely thin tape thickness, so that press marks by the edge portions of the touch roll are produced by the touch roll being thrust against the magnetic tape thus affecting the playback waveform.
For overcoming such inconvenience, the touch roll has its upper and lower ends chamfered. However, with the chamfered touch roll, the constant pressure force, operating on the video tape substantially uniformly at a contact portion with the video tape, is suddenly changed at a point of separation of the touch roll from the video tape as a boundary. Such abrupt changes in the thrusting force produce press marks of the touch roll on the video tape.
For example, with the tape reel having a flangeless reel not having flanges on the upper and lower surfaces of the hub, the touch roll shape is not controlled by the facing distance between the flanges, so that it becomes possible to thrust a touch roll having a longer axial length than the width of the video tape against the entire range along the width of the video tape. The press mark is less liable to be produced if the video tape is of a larger thickness as in the case of the video tape for open reel. However, such flangeless reel or a video tape having a larger thickness cannot be adopted for a digital video tape cassette for business use.
On the other hand, a tape reel is integrally molded with upper and lower flanges from a synthetic resin material in view of productivity, weight and dimensional accuracy. The hub portion of the tape reel has a draft in view of mold release properties. The draft of the hub portion is designed so that it is slightly smaller in diameter towards the flange since the lower flange by which the tape reel is contacted with the reel block is used as a reference surface.
Thus, even if the magnetic tape is wound on the tape cassette in good order under the uniform thrusting force on the outer peripheral surface of the hub portion by the device for taking up the video tape in a good condition, the video tape tends to be subjected to a force of restoration by being contracted due to changes with lapse of time as a result of prolonged storage. The tightening pressure on the hub portion acts with a strong force and a weak force at a larger diameter portion and a smaller diameter portion of the hub portion, respectively. Thus the video tape is deteriorated more significantly at the lower flange portion designed as a larger diameter portion.
For removing air inclusion between respective turns of the video tape taken up on the tape reel for prohibiting the creasing or misregistration between neighboring turns of the tape, it suffices to exert a larger trusting force by a touch roll for taking up the tape on the tape reel. Thus a device for taking up the video tape in a good condition has been proposed in which plural protrusions are formed on the outer peripheral surface of the touch roll for exerting a locally large force on the video tape while a constant thrusting force on the tape is maintained. However, since the video tape is subjected to unequal forces between the points contacted by the protrusions and those contacted by the plain portions, as the tape is taken up, the tape undergoes changes in profile thus deteriorating the playback output.